Novak, 77, said yesterday that the diagnosis was made Sunday and that he was admitted to Brigham and Women's Hospital in Boston, where he will soon begin treatment. "I will be suspending my journalistic work for an indefinite but, God willing, not too lengthy period," he said in a statement.

"He is talking," said an assistant, Amanda Carey. "Everyone's optimistic right now. He's in good spirits." Novak's office said no tests had yet determined whether the tumor was malignant. He became ill when he and his wife went to visit their daughter near Cape Cod, Mass.

Last week, while driving his black Corvette, Novak hit a homeless pedestrian at a downtown Washington intersection. He said he did not realize he had struck anyone until a passing bicyclist stopped him. The 86-year-old pedestrian suffered minor injuries, and Novak received a $50 ticket.

Novak has had cancer diagnosed at least three times, and in 2003 underwent surgery to remove a cancerous growth on his kidney.

The conservative commentator launched a column in 1963 with his longtime partner, the late Rowland Evans, and continued the column, which is carried by The Washington Post, after Evans retired in 1993. The column became more ideological as Novak began moving to the right later in the 1960s.

Although Novak is a pugnacious figure who revels in his "Prince of Darkness" nickname, friends and colleagues describe him differently. "He's a lot nicer than he ever comes across on the screen," said Jack Germond, a retired liberal columnist and frequent sparring partner.

"I came to really respect and admire the guy -- not easy," said MSNBC commentator Tucker Carlson. "He's the toughest human being I've ever met in my life. Nothing bothers him." Carlson recalled seeing Novak deck a protester who had called him a traitor and shoved him in New Hampshire four years ago. "He just kept walking and didn't look back," Carlson said.

Novak was a CNN commentator for 25 years, co-hosting the program "Crossfire" and serving as a panelist on "Capital Gang." He left the network three years ago after uttering a curse word and walking off the set. He is now an analyst for Fox News.

Novak became a lightning rod for criticism in 2003 when he identified Valerie Plame, the wife of administration critic Joseph C. Wilson IV, as a covert CIA operative. Novak obtained the information from Richard L. Armitage, then a State Department official, and confirmed it with Karl Rove, then a senior White House aide to President Bush, without identifying them. The column triggered a lengthy investigation that led to the perjury and obstruction-of-justice convictions of Vice President Cheney's former top aide, I. Lewis "Scooter" Libby, whose sentence was commuted by the president.

Novak's most vociferous critics accused him of treason, and he received a steady flow of hate mail and threats. "What was frustrating was that there were a lot of crazy things being said, that I had taken the Fifth Amendment or that I had made a plea bargain. . . . It's obviously caused me a lot of trouble," he said in a 2006 interview. "If I had it to do all over again, would I have done it? It's a hard question to answer."

Brit Hume, Washington managing editor for Fox News, said Novak has never lost his enthusiasm for reporting. "He has very distinct and well-known political preferences -- he's a strong conservative -- but an absolutely cold-blooded and dispassionate analyst of the state of political races," Hume said. "He's a reporter to his core."